Every known return-flow wind tunnel contains a confuser, a test section, a diffuser, a blower unit, one or several return channels, and turning bends that are used to form a closed loop. The turning bend may be designed as a smooth arc-shaped section for turning airflow through 180 degrees [1, p. 64] or as an elbow bend for turning airflow through 90 degrees. In the latter case, the air channel section between the first turning bend and the second turning bend may be designed with a cylindrical or prismatic cross-section [1, p. 60] or as a diffuser section.
The most close to the proposed wind tunnel is a return-flow wind tunnel containing a confuser, a test section, a diffuser, a return channel, a blower unit, and four 90-degree turning bends with the diffuser section arranged between the first turning bend and the second turning bend [2, p. 11].
The disadvantage of the prior art wind tunnel is a significant air pressure loss due to an inefficient arrangement of the wind tunnel elements. The first turning bend and the second turning bend are main sources of the air pressure loss in the wind tunnel circuit and induce a large air pressure loss in the diffuser. This feature is due to the fact that, in order to reduce the air pressure loss in the turning bends, it is necessary to reduce the airflow velocity in the turning bends by increasing the area ratio of the diffuser. As a result, the air pressure loss in the diffuser would increase. Additionally, the increase of the area ratio of the diffuser is associated with the increase of the length of the diffuser and, as a result, with the increase of the overall dimensions of the wind tunnel and the increase of materials consumption in constructing the wind tunnel.